This invention relates to a method of growing a layer of material on the surfaces of a plurality of substrates placed in a reaction vessel by the chemical vapor deposition technique.
In the field of manufacturing semiconductor devices, it is a well known technique to grow a thin layer of silicon or the like on a semiconductor substrate of silicon or the like, or on an insulating substrate of sapphire or the like by use of the chemical vapor deposition (CVD) technique. In the CVD technique, it is desirable to place as many substrates as possible in a reaction chamber and grow on all the substrates a layer of a uniform thickness and a uniform characteristic (for example, uniform resistivity).
In general, the following processes by the CVD technique have been employed so far in order to grow a layer of material. A number of substrates are arranged on a plate-like susceptor in a reaction chamber and heated at a high temperature. Under this condition, a reaction gas is supplied from the inlet of the reaction chamber to the substrates so that a layer of material is grown thereon, and then the gas is exhausted from the exhaust of the reaction chamber.
In such method, however, increase of the number of substrates per batch will tend to make the thickness and resistivity of a layer of material on the substrates ununiform. For example, when thirty substrates of three-inch diameter each were arranged on the plate-like susceptor and processed as described above, the thickness was scattered in value to about 15% and the resistivity to as much as 20%. This cause will be considered that as the reaction gas supplied from the inlet of the chamber approaches to the exhaust, the concentration of the gas decreases due to the growth of a layer of material.
Up to date, different proposals have been made in order to increase the number of substrates per batch to be processed with a layer of material kept uniform. For example, in the U.S. Pat. No. 4,082,865, issued to Ban et al. on Apr. 4, 1978, there is disclosed a method that a plurality of substrates are placed in a reaction chamber in stack-like arrangement and a reaction gas is supplied from a plurality of gas nozzles to the substrates to grow an improved uniform thickness of layer. Also, in the U.S. Pat. No. 3,461,836, issued to Henker on Aug. 19, 1969, there is disclosed another method in which a plurality of substrates are arranged on a plate-like susceptor in the reaction chamber, a reaction gas is similarly supplied from a plurality of gas nozzles to the substrates to form an improved uniform thickness of layer.
In these methods, however, it is necessary to sweep the gas nozzles back and forth in an arc or rotate the substrates in stack-like arrangement, this making the mechanism of the growth apparatus complicated. Moreover, in these methods, it is impossible to control the concentration of the reaction gas at each position within the reaction chamber during the CVD process, and therefore the reproducibility of a layer of material is uncertain when the substrate arrangement is changed.